From the few rounds I've tried..it's decently fun and what we've come to expect from Triniti games (which I've usually had fun with). It feels just like Zombieville 2 right now, but with different missions. There's survive for time limit, kill x number of zombies, protect something for time limit. There looks to be other type of missions as well..and while I'm not sure how varied they are, it's a nice change from the lack of missions in Zombieville 2. There looks to be a decent number of weapons with the usual upgrade system. I haven't played long enough to see how varied the enemies are yet.
One negative is it looks like you always need to have Internet connection to even get to the main menu screen. I tried turning airplane mode on, an it wouldn't even get to the main menu screen. The level loading times feels long too.
Otherwise, the game is decently fun, and exactly what you expect from. Thanks for the promo code.